Electrical measuring instrument.



L. T. ROBINSON & O. HOLZ.

M. D. HOLZ, nxsoumux or 0. HQLZ. nzo'n. ELECTRICAL MEASURING INSTRUMENT.

v APPLICATION FILED JUNE 9, 1909. I 1,057,276. Patented Mar. 25, 1913.

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i Q J :9! I i L Q I Inventors: I Witnesses: q LewlsTfiobmson,

COLUMBIA PLANoflRAPH co.,WAsHINoToN, D. c.

UNITED STATES PATENT oEEIoE.

LEWIS T. ROBINsON, 0F SCHENECTADY,-NEW YORK, AND OTTO I-IOLZ, DECEASED,BY

MATIE D. HOLZ, EXECUTRIX, or soHENEcTAng Ew YORK, ASSIGNORS To GEN- ERALELECTRIC COMPANY, A CORPORATION OF NEW YORK.

ELECTRICAL MEASURING INSTRUMENT.

To all whom it may concern.

Be it known that I, LEWIS T. ROBINsON, a citizen of the United States,residing at Schenectady, county of Schenectady, State of New York, didjointly with OTTO I-IoLz, deceased, invent the certain new and usefulImprovements in Electrical Measuring Instruments set forth in thefollowing specification; and be it also known that I, MA- TIE D. HOLZ, acitizen of the United States, residing at Schenectady, county ofSchenectady, State of New York, eXecutriX of the estate of OTTO I-IOLZ,deceased, late a citizen of the United States, am informed and believethat the said OTTO How did jointly with LEwIs T. ROBINSON invent thecertain new and useful Improvements in Electrical Measuring Instrumentsset forth in the following specification.

This invention relates to electrical measuring instruments, and moreparticularly to instruments for indicating the ratio between theeffective voltage and average voltage of an alternating current circuit,this ratio commonly being known as the form factor of the wave ofcurrent.

One of the most important tests in connection with the manufacture anduse of transformers is the determination of the core loss, but sincethis loss varies through wide limits when the same transformer is usedon circuits having different wave shapes, it is desirable to determinewhat the core loss of a transformer will be when supplied with currentof a given wave shape. For various reasons the sine wave is mostdesirable for general use and is the wave produced by most moderngenerators, and it is,

therefore, convenient to use the core loss occurring on a sine wave as astandard of comparison, but the transformers must often be tested orused withcurrent having a different wave shape. The core loss in atransformer consists of two components, one due to hysteresis and theother due to eddy currents of the iron of the transformer, and both ofthese components are affected by a change in wave shape. It has beenfound that the core loss in a transformer is dependent upon the formfactor of the wave, or, in other words, the ratio of the effectiveelectromotive force to the average electromotive force. It has beenfound by test and calculation that if. the core loss due Specificationof Letters Patent.

Application filed June 9, 1909.

Patented Mar. 25, 1913.

Serial No. 501,210.

to a current or having a definite wave form be determined, then the coreloss due to another current I) having a different wave form is equal tothe core loss produced by a multiplied by a fraction formed by the formfactor of a over the form factor of I), this fraction being raised tothe 1.6 power; therefore, observations taken on any transformer by meansof a wave of one shape may be corrected to apply to the same transformerwhen excited by current having a different wave shape, and the resultswhich will be obtained by any wave shape may be accurately predicted.

In order to carry out the comparison of the core loss due to current ofone wave shape with the loss produced by a different wave shape, theform factors of both waves must be known, and the object of thisinvention is to produce a simple and accurate instrument which willindicate directly the form factor of the current wave of any alternatingcurrent circuit to which it may be applied, and by means of which thedata for making the comparisons above described may be quickly andeasily secured.

In carrying out this invention, the form factor is determined by causingthe indication of the instrument to be the resultant of the effectiveelectromotive force and of the average electromotive force; effectiveelectromotive force in this specification meaning the square root of themean square value or the value indicated by an alternating currentvoltmeter.

The invention is preferably embodied in some form of instrument havingan indicatin'g'element which is free to move without restraint andhaving means which tend to move theindicating element in one directionto an extent dependent on the effective voltage, and means which tend'to move the indicating'element in the other direction to an extentdependent on the average voltage, both of said means tending to movesaid element through an equal range of movement. The preferred form ofinstrument comprises essentially an alternating current voltmeter, whichindicates the effective value of the electromotive force and tends toturn a pivoted indicator in one direction through a definite range, suchas while another device, which indicates the average electromotive forceacts upon 7 the same indicator and tends to turn it in range of 90. Thepreferred form of de vice for indicating the average voltage comprises avoltmeter which responds to unidirectional potential, this potentialbeing dependent upon the potential of the alternating current circuit ofwhich the wave shape is to be investigated, and being derived from thatcircuit by some suitable rectifying device, such as a rectifyingcommutator driven by a synchronous motor.

This invention will best be understood in connection with theaccompanying drawings, which illustrate one of the numerous forms inwhich it may be embodied and in which Figure 1 illustratesdiagrammatically one form of device in which the invention may beembodied, and Fig. 2 illustrates a modified form.

In the particular arrangement shown in Fig. 1, the main leads 1 of thealternating current circuit, of which the form factor is to bedetermined, are connected through a regulating resistance 2 to supplyleads 3 on which the voltage may be adjusted to any desired value bymeans of the regulating resistance 2 and read by means of a voltmeter4:. The effective value of the alternating electromotive force on thesupply leads 3 acts upon any suitable device, such as an'alternatingcurrent voltmeter 6 provided with a moving coil 7 mounted on a freelymovable indicating shaft or member 8 provided with an index or pointer9, which swings over a suitable graduated scale 10. The shaft or movablemember 8 is preferably pivoted and is free to turn into any angularposition without being restrained by a control spring, and hence is freeto take up any position of equilibrium.

In order to obtain the form factor or ratio between the effective valueand the average value of the alternating electromotive force on thesupply leads 3, suitable means are provided for subjecting the indicatorshaft or movable member 8 to a counter-torque opposed to that exerted bythe alternating current voltmeter 6 and directly dependent upon theaverage voltage of the electro-motive force on the leads 3.

Various devices may be used for exerting the opposing or counter-torquedependent upon the average voltage, the preferred device being, as shownin Fig. 1, a undirectional voltmeter comprising a permanent magnet 11for producing a constant magnetic flux through the air gas between thepole pieces of the magnet and an iron core 12, and a current-carryingcoil 13 mounted on and rigidly connected to the indicating shaft ormember 8 to oppose the action of the alternating current voltmeter 6.The torque exerted by the coil- 13 is made dependent upon the averagevoltage on the supply leads 3 by means of a suitable connections, suchas leads 14 which join the coil 13 to the brushes 15 of a rectifyingcommutator 16, to which current is supplied from the alternating currentcircuit by means of brushes 17 the commutator being driven at the properrate by a synchronous motor 18 connected to the main leads 1. It isobvious that any suitable form of rectifying device may be used tosupply current to coil 13, and the rectifying commutator driven by thesynchronous motor is shown merely for the purpose of illustration. Sincethe instruments respond to voltage, the coils are preferably highresistance coils, although the amount of current through them can becontrolled by the use of suitable resistance in series.

The operation of the form of instrument shown in Fig. 1 is as follows:The instrument is connected to the main leads 1 when the form factor ofthe current wave on those leads is tobe determined, and by means of theadjusting resistance 2 the voltage on the leads 3 is brought to thedesired point. The alternating current voltmeter 6 now tends to turn theindicating shaft 8 and pointer 9 into a position dependent upon theeffective voltage upon the supply leads 3, while the rectified currentsupplied from the leads 3 to the coil 13 of the unidirectional voltmetercauses the coil 13 to tend to turn the indicating shaft in the oppositedirection into a position dependent upon the average voltage. The resultof those opposing forces is that the indicating shaft 8 and theindicator 9 take up a position which is a resultant of both theeffective voltage and the average voltage of the alternatingelectromotive force on the supply leads 3, and this position ives theform factor of the alternating e ectromotive force which is beinginvestigated. If the form factor of the wave on the main leads 1 issecured in this manner, the core losses of transformers connected withthis circuit may be easily calculated if their core losses on a wave ofdifferent shape have been secured.

Under some conditions it is desirable to simplify the instrument, andfor this purpose the modified form shown in Fig. 2 may be used, inwhich, as above, the main leads 1 are connected through an adjustingresistance 2 to an alternating current volt meter 6, which tends to turnthe indicating shaft 8 in one direction into a position dependent uponthe effective voltage, while at the same time a counter-torque isexerted upon the shaft 8 by means of a device which exerts a torquedependent on the average voltage, this device comprising an iron vane19, which is of such small section that it is practically saturated andwhich cooperates with coils 20 connected in series across the mainleads 1. By properly proportioning the vane 19, the torque exerted by iton the indicating shaft 8 in opposition to the torque of the alternatingcurrent voltmeter 6 may be made practically proportional to the averagevoltage of the alternating electromotive force on the main leads 1.

By proper calibration the instrument may show directly on its scale coreloss in terms of the loss due to any selected wave, since the lossesvary in proportion to the 1.6 power of the form factor, and by raisingthe angle represented by a given form factor to the 1.6 power andmarking the resultingangle on the scale suitable calibration may beobtained to give the loss directly.

This invention may be embodied in many other forms than that shown anddescribed herein, and we, therefore, do not Wish to restrict ourselvesto the arrangement herein disclosed, but aim in the appended claims tocover all modifications within the spirit and scope of the abovedescribed invention.

WVhat we claim as new and desire to secure by Letters Patent of theUnited States, is-

l. A form factor indicator for alternating current circuits, comprisingin combination two relatively movable members, and means for producingon the movable member a torque dependent on the average voltage of thecircuit and a counter-torque dependent on the effective voltage of thecircuit.

2. In a form factor indicator for alternating current circuits, thecombination with an unbiased pivoted indicating member, of means forderiving from an alternating current circuit a torque which is exertedon said member to rotate it in one direction and is dependent on theaverage voltage of the circuit, and means for deriving from the samealternating current circuit a torque which is exerted on said member torotate it in the opposite direction and is dependent on the effectivevoltage of the circuit.

3. In a form factor indicator for alternating current circuits, thecombination with a voltmeter responsive to the effective voltage of analternating current circuit of a second voltmeter responsive to theaverage voltage of an alternating current circuit, an indicating shaftcommon to both said voltmeters and mounted for unrestrained movementinto any angular position, and means for connecting both said voltmetersto an alternating current circuit to exert opposing torques on saidindicating shaft. 7

4. A form factor indicator for alternating current circuits comprisingtwo current-carrying coils, an indicating member carrying said coils andmounted to turn freely into any angular position, means for producing amagnetic flux through both said coils, and means for connecting saidcoils to an alternating current circuit to cause said coils to exert onsaid member opposing torques, one dependent on the effective voltage andthe other dependent on the average voltage of the alternating currentcircuit.

5. In a form factor indicator for alternating current circuits, thecombination with an alternating current voltmeter, of a unidirectionalcurrent voltmeter, an' unbiased pivoted indicating member actuated byboth voltmeters, a rectifying device connected to said unidirectionalvoltmeter, and means for connecting said rectifying device and saidalternating current voltmeter to an alternating current circuit to causesaid voltmeters to exert opposing torques on said indicating member.

In witness whereof, we have hereunto set our hands this 8th day of June,1909.

LEWIS T. ROBINSON. MATIE D. HOLZ, Ewecutm'm of the estateof Otto H022,de-

ceased.

Witnesses:

BENJAMIN B. HULL, ANNA H. WAGNER.

Copies of this patent may be obtained for five cents each, by addressingthe Commissioner of Patents, Washington, D. G.

